In Outlook 2007 you must go to folder view (at the bottom, click the Folder icon on the lower left)
Go to Contacts in the folder list
Right click each contact group, Outlook Address Book Tab, Show in Address Book check.

This Experts Exchange video Micro Tutorial shows how to tell Microsoft Office that a word is NOT spelled correctly. Microsoft Office has a built-in, main dictionary that is shared by Office apps, including Excel, Outlook, PowerPoint, and Word. When …

This video shows how to remove a single email address from the Outlook 2010 Auto Suggestion memory.
NOTE: For Outlook 2016 and 2013 perform the exact same steps.
Open a new email: Click the New email button in Outlook.
Start typing the address: …